Recently, solar photovoltaic power generation using crystalline silicon solar cells passes a test stage and attains a commercialization stage due to advantages thereof such as pollution-free, safety, high performance, and reliability.
As a result thereof, in several nations such as German, Japan, and Korea, high capacity of solar photovoltaic power generation is performed to several thousands to several ten thousands kW.
Currently, solar cells used in solar photovoltaic power generation are manufactured generally using one of single crystal ingots manufactured by Czochralski method and polycrystal silicon ingots manufactured by Bridgman method. To continuously increase large-scale capacity and economical feasibility, it is considered to more lower the cost of silicon ingots and substrates and to increase productivity.
On such grounds, particularly, there are provided a lot of efforts to efficiently produce polycrystal silicon ingots whose properties are not largely deteriorated rather than that of single crystals, capable of reducing cost thereof.
Manufacturing polycrystal silicon ingots for a solar cell basically has “directional solidification” as properties.
A crucible manufactured using one of quartz and graphite is filled with raw silicon for solar cells. The raw silicon is melted at a temperature of 1420° C. or more and heat of solidification of silicon is removed in a certain direction toward a bottom of the crucible, thereby spreading solidification from the bottom of the crucible to a top of the crucible, which is a directional solidification process.
Ingots obtained as a result of a well-controlled directional solidification process has a columnar structure in which a large number of single crystal columns are coupled with one another in one direction in such a way that there is provided a structure capable of collecting electrons generated by photos toward an electrode without loss, identical to single crystals, when manufacturing a substrate vertical, to a crystal growth direction.
General polycrystal silicon ingots for solar cells with commercial scale have a size of about 400 to 450 kg. To embody high quality, general polycrystal silicon ingots are manufactured one by one at a time in a batch. Generally, there are required a long process for two days or more, a large amount of power consumption, and expensive installation costs.
Technical core is to manufacture polycrystal ingots suitable for solar cells by melting and directionally solidifying raw silicon, whose crystal structure is a columnar structure, whose grain size is large, having a high quality, in which crystalline defects and impurities are less enough.
To embody this, it is required to accompany an optimal design for a heater forming a hot zone of an apparatus for manufacturing ingots, an insulator, a bottom heat transfer system for directional solidification, inert gas, a vacuum system, coated crucibles, a system against a leakage of melted silicon, and optimization of variables in process such as silicon melting and solidification speed and heat treatment speed.
Technical developments in the art have focused on embodying the quality of ingots and also increasing productivity and economic feasibility by promoting improvements in such apparatuses and processes.
In such situation, a primary direction of present technology development is to more increase a size of ingots produced in a batch at a time. However, as another way to increase productivity and reduce cost, there may be considered a way of producing a plurality of ingots in a batch at a time. Thereupon, an aspect of the present invention is to provide a new apparatus for manufacturing ingots and a method of using the apparatus, the apparatus capable of producing a plurality of ingots simultaneously with the same process time, and to provide additional technologies according thereto.